class Bird():
    def __init__(self):
        pass    
    def eat(self, sta=0):
        if sta == 0:
            print("我要吃东西")
        else:
            print("我还不饿")
    def sing(self, singname):
        print(singname)

a = Bird()
a.eat()
a.eat(1)
a.sing("叽叽叽叽")